The theory of constraints (TOC) has all of the following perspectives of inventory except: 

a. Inventory slows down the production process, leading to delayed or even lost sales. 

b. Unneeded inventory is a costly investment that doesn't generate an income return. 

c. Inventory is not an asset in the production process, but is often a barrier to achieving the organization's main goals. 

d. Inventory highlights problems with quality.